Solve for $k$ : $15 + k = -9$
Solution: Subtract $15$ from both sides: $ \begin{eqnarray} \\ 15 + k &=& -9 \\ \\ {-15} && {-15} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{15 + k} &\hphantom{=}& \hphantom{-9} \\ k &=& -9 {- 15} \\ \end{eqnarray} $ Simplify. $ k = -24$